我自己已经找到解决办法了,分享一下

   var query = DB.FullClient.Queryable<ContractOrders, Contracts>((co, cs) => new object[]{

                JoinType.Inner,co.ContractId==cs.Id

            })

            .WhereIF(!string.IsNullOrEmpty(customerId), (co, cs) => cs.CustomerId == customerId)

            .WhereIF(startDate.HasValue, (co, cs) => cs.ActivateDate >= startDate.Value)

            .WhereIF(endDate.HasValue, (co, cs) => cs.ActivateDate <= endDate.Value.AddDays())

            .WhereIF(status.HasValue, co => co.Status == status.Value)

            .Select((co, cs) => new ContractOrdersP<Contracts>

            {

                Code = co.Code,

                Id = co.Id,

                CreateTime = co.CreateTime,

                ContractId = co.ContractId,

                Remark = co.Remark,

                Status = co.Status,

                Contracts = cs,

                TotalPrice = SqlFunc.Subqueryable<ProductConfigs>()

               .Where(r => r.ContractOrderId == co.Id)

                .GroupBy(r => r.ContractOrderId)

                .Select(r => SqlFunc.AggregateSum(r.Quantity * r.DiscountPrice))

            });

用这个函数可以解决, SqlSugar作者 定义了AggregateSum 这种方法, 一般人还真不知道

.x

.Max(it => it.id);

.Sum(it => it.id);

 //子查询的版本

                var list = db.Queryable<TC020_Purchase>()

                        .Select(a => new

                        {

                            guid = a.TC020_Guid,

                            compony = a.TC020_Company,

                            SignDate = a.TC020_SignDate,

                            ProjectTitle = a.TC020_ProjectTitle,

                            Signer = a.TC020_Signer,

                            ContractID = a.TC020_ContractID,

                            PaymentClaus = a.TC020_PaymentClause,

                            TotalCount = a.TC020_TotalAmount,

                            paid = SqlFunc.Subqueryable<TC022_PurchasePaymentRecord>()

                                .Where(b => b.TC020_Guid == a.TC020_Guid)

                                .Select(b => SqlFunc.AggregateSum(b.TC022_NotPaid.Value)).ToString(),

                            notpaid = SqlFunc.Subqueryable<TC022_PurchasePaymentRecord>()

                                .Where(b => b.TC020_Guid == a.TC020_Guid)

                                .Select(b => SqlFunc.AggregateSum(b.TC022_Paid.Value)).ToString()

                        }).ToList();

  //Group by 版本

                var group = db.Queryable<TC020_Purchase, TC022_PurchasePaymentRecord>((a, b) => new object[] {

                            JoinType.Left,a.TC020_Guid==b.TC020_Guid})

                        .GroupBy(a => new {

                            a.TC020_Guid,

                            a.TC020_Company,

                            a.TC020_SignDate,

                            a.TC020_ProjectTitle,

                            a.TC020_Signer,

                            a.TC020_ContractID,

                            a.TC020_PaymentClause,

                            a.TC020_SalesContractID,

                            a.TC020_TotalAmount

                        })

                        .Select((a,b)=> new {

                            paid=SqlFunc.AggregateSum(b.TC022_NotPaid.Value).ToString(),

                            notpaid= SqlFunc.AggregateSum(b.TC022_Paid.Value).ToString()

                        }).ToList();